1. Field of the Invention
The present invention relates to a method of managing electric energy consumption and/or production dynamics and a device therefor.
2. Present State of the Art
Energy flows in an electric network are not constant with time. At each moment of time, the balance between consumption/demand and production/offer of electric energy in the network is managed by automatic control systems, which process various measures of electrical quantities.
Electronic electricity metering devices are known in the art, which sample electric energy at a high time resolution to obtain instantaneous current and voltage values, and to total/add up the amount of energy flow, and transmit it into the network at regular time intervals (“time-driven” method). This method uses a communication channel through which a given data volume is exchanged between the above mentioned devices and a mainframe located within the network.
Among the various electrical quantities, such as voltages, currents, frequencies, angles/phases, the amounts of energy have a key role. The amount of metered electric energy, which always accounts for the basic components of which it is composed, may be expressed as the arithmetic sum of instantaneous values times the measurement time, according to the formula:
      E    =                            ∫          0          t                ⁢                                            V              ⁡                              (                t                )                                      ·                          I              ⁡                              (                t                )                                              ⁢                                          ⁢          d          ⁢                                          ⁢          t                    ≈                        ∑                      i            =            0                    t                ⁢                                  ⁢                  [                                                    V                ⁡                                  (                                      t                    i                                    )                                            ·                              I                ⁡                                  (                                      t                    i                                    )                                            ·              Δ                        ⁢                                                  ⁢            t                    ]                      ,where V(ti) is the instantaneous voltage value at time ti, whereas I(ti) is the instantaneous current value at time t, and Δt=[ti−ti−1].
With t equal to 15 minutes, what has happened in the recent past can be observed. Assuming that t is 0.1 seconds, electrical events are captured but such knowledge cannot be shared over the network. The factor t sets the trade-off between visibility of electrical processes in their details and the data volume exchanged over the network. In prior art, fiscal electronic electricity meters consolidate the past energy over long time intervals into increasing positive “units”, expressed in kWh.
Digital electronic electricity metering devices use the above discrete formula to calculate instantaneous energy values upon which the amount of cumulative energy delivered is in turn calculated (an example of such process is described in www.xylenepower.com/Electricity Metering.htm). The accuracy of the numerical calculation in the discrete space is ensured by a high sampling rate.
Various types of electricity metering devices are known and commercially available. One example of such devices is the electronic meter sold by ENEL, an Italian-based company, which is used in the “Telegestore” system (e.g. see www.enel.com/it-IT/innovation/smart_grids/smart_metering/telegestore).
Typically, an electricity metering device comprises an analogue current and voltage sensing module, a microchip, a digital metering software code implemented in the microchip, a power supply, a communication module for network transmission of the metered values and memory means.
Prior art electricity metering devices are available and used for detecting past values only, such as power consumption data or power generation data at the electric company customer sites with which the metering device is associated. The electricity metering device is owned by the electric company, and the user is allowed no real-time data access. Electronic electricity metering devices measure instantaneous power consumptions in real time, total them and save the consolidated values (units) in the local memory of the electronic metering device, thereby making such values persistent as stored and with no further processing.
Then, the local values are requested by the electric company for billing and alignment of the electronic metering devices, and then said values are transmitted. This usually occurs upon request, with a certain rate, and at predetermined time instants, i.e. in “time-driven” mode. For synchronization of the remote electronic metering devices with those located at the electric company, there is a step in which data are transmitted to the electric company using standard communication protocols, mainly at delayed times. Generally, data transmission may occur in “push” or “pull” mode, i.e. spontaneously or upon request. Prior art electronic meters use the “pull” mode: the electric company queries a device to receive a response.
The metered values are incremental, are typically sampled every 10-60 minutes and are used for billing purposes. Such time window is selected to contain the data volumes to be transmitted, and make them fit for billing, but this makes them unusable for real-time load balancing. For instance, the Italian Telegestore performs data sampling by consolidating measurement every 15 minutes. A meter measures the past behavior of the network node, does not qualify current processes on a given node, does not estimate their future development and does not qualify the state of the node.
Two relevant meter classes are: (a) spectrum analyzers that measure present energy quality parameters and (b) industrial and/or mass-market panel meters, which make their data available over the web, such as WEB-MX (www.energytracking.com) e FEMTO (electrex.it/prodotti/contatori-analizzatori).
These classes of metering devices operate in “slave” mode, make their data available upon request in “pull” mode, and use short-range (WiFi) and/or web-based (Internet IP/FTP/SMTP/POP3/SNTP and others) communication protocols for data communication.
These devices cooperate with another server (master) device for time-driven control at intervals typically longer than 1 minute, but do not support the real-time decision process, because they do not always deliver data on time. Pull mode data requests of serial communication protocols involve a given waiting time to receive the result, which time is always a multiple of the request time (three times in Modbus). Due to this peculiar feature, there will be periods of time in which network events cannot be observed.
Phasor measurement units, or PMU, are also known, which have a real-time operation and transmit digitized values of energy vectors (Phadke, A. G., “Synchronized phasor measurements—a historical overview,” Transmission and Distribution Conference and Exhibition 2002: Asia Pacific. IEEE/PES, vol. 1, no., pp. 476-479 vol. 1, 6-10 Oct. 2002). Adjustment of power flows in the transmission network segments is based on the observation of the difference between phasors on both sides (of the segment). This occurs in perfect synchronism over a small number of main segments of the electric network, using GPS devices and restricting use to “outdoor” locations, where satellites (GPS, Galileo, Glonass and the like) are visible. The key feature of the method that uses phasors consists in simultaneously observing pairs of network nodes using PMUs, each of which observes electrical values, calculates phasors and transmits data over the network at a very high rate. This allows comparison of “input” and “output” energy flows on a given circuit segment. Then, a PCD (“Primary Domain Controller”) is used to calculate the differences and analyze said combination of values in an intelligent manner, with rules being applied to check for any anomaly. While PMU devices cooperate together, they measure instantaneous observations and cannot handle historical dynamics. PMUs estimate the current state of the system, but are not autonomous in doing so, as they require the presence of a PDC intelligent device which receives combined data pairs and processes them.
PMUs perform intensive calculations by real-time computation of phasor values, but the latter only remain valid during steady-state of the electric system. In the prior art, software procedures are used to characterize and manage energy variations, to log their history and make state changes which procedures impart intelligence to control schemes.